Cast alloy



May 11 1965 J. R. KoNEcsNl 3,183,082

CAS'l ALLOY Filed Jan. 22, 1962 :fasc/ah E. Ha/femm' The present invention relates to an improved alloy composition. The alloy compositions of the present invention find particular utility in the field of valves for internal combustion engines.

A great deal of work has been done in the field of finding suitable corrosion resistant materials for the manufacture of valves to protect them against burning by the combustion products evolved by the ignition of gasolines containing leadl compounds. Various corrosion resistant facings have been applied to those portions of the valve which aremost subject to lead oxide corrosion. Attempts have been made to provide corrosion resistant alloys which can be used in the as cast condition to elminate the necessity of applying facings. These efforts have resulted in some degree of success but frequently the improvements achieved in providing resistance to lead oxide corrosion were made at the expense of other desired physical properties in the valve such as impact strength, hot strength, and hot hardness. The provision of an alloy composition which not only has improved burning resistance, but also has improved impact strength, hot strength, and hot hardness is the principal object of the present invention.

A further object of the present invention is to provide an improved alloy which can be used for the manufacture of valves, turbine parts, and the like in the as cast structure thereby eliminating expensive working and facing operations.

Another object of the invention to provide an irnproved internal combustion engine valve employing the alloys of the present invention.

A further object of the invention is to provide an internal combustion engine valve having increased burning resistance at the top of the head of the Valve, where corrosion has been particularly troublesome.

The alloys of the present invention are nickel-cobaltchromum alloys which are characterized by their ability to form a spinel structure under the conditions of operation to which they are subjected during use. These alloys are substantially iron free, although amounts of iron up to can be tolerated, and such small amounts are unavoidably present in the metals making up the alloy. The presence of larger amounts of iron is undesirable because it tends to form a solid solution of Fe2O3.Cr2O3 which affords very little corrosion protection in a metal oxide atmosphere.

There are several avenues of approach in securing the desired spinel structure from the alloys of this invention. One is to eliminate substantially any carbon since carbon combines with chromium to form carbides, thereby making some of the chromium unavailable for spinel formation. However, li consider it preferable to have some carbon present in the alloy for its other beneficial effects (improving hardness and lluidity) and thenadd suicient chromium so that suicient chromium remains,

` after carbide formation, tolfo'rm the desired spinel.

ice

unavoidable impurity, in amounts up to about 5% to act as a deoxidizer. Silicon is also unavoidably present as Y An even more preferable compensation for carbon resides in `adding strong carbide formers such as tungsten topreferentially react with the carbon, thereby permitting the chromium to remain free for spnelformation.

'Ihe'alloys of the .present invention may also contain molybdenum for the purposes of strengthening the alloy. Manganese. may be added, either intentionally or as an an impurity and can be tolerated up to about 2% since it also acts as a deoxidizer. In the event that the naturally occurring deoxidizers are present in insufficient amounts, additional deoxidizers such as calcium and aluminum can be added in amounts up to about l/2%. With the foregoing in mind, the alloys of this invention which exhibit the best properties have compositions within the following ranges:

Table I Carbon 0.50 to 2.50% by weight. Manganese 5.00% maximum. Silicon 2.00% maximum. Chromium 15.00 to 30.00%. Nickel 20.00 to 35.00%. Iron 5.00% maximum. Molybdenum 1.00 to 10.00%. Tungsten 1.00 to 10.00%. Cobalt Substantially the balance.

Within the broader ranges expressed' above, the particularly preferred alloys of the present invention have the following ranges of compensation:

Table Il Carbon 1.50 to A1.80% by weight. Manganese 0.50% maximum. Silicon 0.50% maximum. Chromium 24.00 to 27.00%.

Nickel 28.00 to 32.00%.

Iron 3.00% maximum. Molybdenum 4.00 to 7.00%.

Tungsten 4.00 to 7.00%.

Cobalt Substantially the balance.

During the development of the alloys of the present invention, it was found that the new alloys, when subjected to conditions of lead oxide corrosion in an engine formed spinel type structures which are highly resistant to further corrosion. These spinels are identified by X-ray techniques and may be represented by the for-y mulae CoO.Cr2O3 and NiO.Cr2O3, and also by an extremely resistant mixed spinel, (Ni,Co)Cr2O4.

It appears that with the compositions of the present invention the particular spinels formed are the most resistant to corrosive attack. That is why, for the purposes of the present invention, it is desirable to keep the weight ratio of cobalt to nickel less than aboutA 2.0 and preferably in the range from 0.8 to 1.2. The ideal alloy, I believe, would have a cobalt to nickel weight ratio of about l to 1. Since the atomic weights of cobalt to nickel are very close, it can be said that the best alloys result when substantially equimolar amounts of nickel and cobalt are used in the alloy composition.

Specific alloy compositions coming within the scope of the present invention are given in the following table:

TheA physical properties of the'new alloys have been tested against high quality valve alloys previously` employed in the 'prior art. Consistently, the new alloys showed an improved resistance to corrosion, particularly at the top of the head of the valve where corrosion has heretofore been very troublesome. The hot strength, tip and stem performance were very satisfactory in all cases.

3 One of the best high quality valve materials heretofore available (Stellite F) was used as a reference in making performance tests. Thisv alloy hasthe following The alloys of the present invention which were used in this test all had compositions within the ranges specified in Table II. Both the reference alloy and the new alloys were cast in shell molds in conventional casting procedures- To evaluate the performance of the new alloys against the reference alloys, a series of split installation, locked valve tests were initiated in a six cylinder Chevrolet Model 235 truck engine. The following table sets forth the test conditions obtaining during these tests:

tion, 2.8-3.0 ml. tetraethyl lead gal.

The test valves and the reference valves were installed' at alternate cylinder positions. Following completion of the first run of each test, a second run was performed with a reverse valve installation. The exhaust valves were positively locked throughout to promote valve burning. In all of the tests, the valves made with the test alloy out performed the valves made with the reference alloy. One test had to be terminated after 169 vhours when one of the reference valves failed by burning. Another run was terminated at 140 hours for the same reason. No test had to be terminated because of burning of any valve made of the test alloy. An examination of the valves from the tests shows that the valves made of the test material were in a better overall condition then the reference valves. Some of the reference valves showed an early stage gutter across the seating surface in addition to light slective corrosion at adjacent areas of the face. Other valves made of the reference material showed incipient channeling, occasional localized pitting at the face periphery and light, selective corrosion. The average lash loss was approximately 60% greater for the reference valves than for the test valves.

Other physical properties of the test alloys of the present invention are listed in the following table.`

posits consist of three overlapping layers.

-1200n F. 7.29 75-l400 F. 7.55 75-1600 F. 7.38

Stress rupture, hours to failure:

30,000 p.s.i. at 1350 F 520.7 20,000 p.s.i. at 1350L7 F 2,265.0 15,000 p.s.i. at 1500 F. 2,556.0 Brinell hardness (750 kg.-5 mm. ball):

Room temperature 368 1400 F. 289 1500 F. 289 1600^F. 238

The microstructure of the alloys in the as cast condition is illustrated in the single figure of the drawings.y

On a reproduction measuring four and one-half inches square, the magnification would be 250 times. The etchant used was a solution of mixed acids. in the figure, reference numeral 10 represents a matrix composed of dendrites, while reference numeral 1l has been applied to the inter-dendritic carbides which exist in the as cast structure.

X-ray diffraction studies were made of the testfvalves after scraping the tops of :the heads, and treating them with a sodium hydroxide solution to remove lead compounds.

Frorn the outside irito the base alloy, these consist'of lead compounds having the formula (PbO)x.(PbCrO4)y, then a layer of spinel (Ni, Co) Cr2O4, and NiCoO2, in that order.

The X-ray diffraction data obtained from anexamination of the valves after the test periods are -given in the following table. The values for nickel spinel and cobalt spinel were obtained from the ASTM Alphabetical and Grouped Numerical Index of X-ray Diffraction Data 1955:

Table VI NCI204 COCI`204 Test Alloy d, A. I/I, d, A. i/Ii d, A. I/Ii 4.79 20 4.84 4 2.94 Medium. 2.93 30 2.94 .33 2.51 Very Strong. 2. 50 100 2. s3 5 2.00 strong. 2.07 35 2. 51 100 1. so weak. 1.70 15 2. 40 4 1.47 Medium. 1. e0 00 2.07 27 1. 47 s0 1.20 2 1.31 10 1.70 19 1.27 25 1.65 1 1.20 10 1. 00 43 1.08 25 1. 47 60 1.31 3 1.27 10 1.20 1 1.11 5 1.08 v 23 1.04 4

The foregoing X-ray data shows that there is a definite spinel formation during engine operation when employing the test alloy valves. That the spinel produced is a nickeli-cobalt spinel having approximately equimolar proportions of nickel and cobalt was shown by checking the` chemical analysis of the valve heads with X-ray fluorescence after lead compounds'had been removed by NaOH solution so that only the oxides remained. Average results of the analysis were as follows:

As indicated From the X-ray data, itappears Athat the'de The above gures for the oxides are relative not absolute percentages. This is because the absorption of oxide for X-rays is not the same as the absorption of the valve alloys or the alloy standards for X-rays.

It will be noted that the Co/ Ni ratio is about 1.

It should be evident that minor variations can be made in the chemistry of the alloys without departing from the scope of the present inventioln.

I claim as my invention:

1. An alloy composition having improved resistance to burning by oxidation products of leaded gasolines consisting essentially of:

Carbon 0.50 to 2.50% by weight Manganese 5.00% maximum Silicon 2.00% maximum Chromium 15.00 to 30.00%

Nickel 20.00 to 35.00%

Iron 5.00% maximum Molybdenum 1.00 to 10.00%

Tungsten 1.00 to 10.00%

Cobalt Substantially the balance the ratio of cobalt to nickel being at least 0.8 to 1 but not more than 2 to l.

2. An alloy composition having improved resistance to burning by oxidation products of leaded gasolines consisting essentially of:

the ratio of cobalt to nickel being at least 0.8 to 1 but not more than 2 to l.

3. An alloy composition having improved resistance to burning by oxidation products of leaded gasoline consisting essentially of:

Carbon 0.50 to 2.50% by weight Manganese 1.00% maximum Silicon 1.00% maximum Chromium 15.00 to 30.00%

Nickel 20.00 to 35.00%

Iron 5.00% maximum Molybdenum 1.00 to 10.00% Tungsten 1.00 to 10.00%

Cobalt Substantially the balance the weight ratio of cobalt to nickel in said alloy being less than 2: 1, but at least 0.8 to l.

4. An alloy composition having improved resistance to burning by oxidation products of leaded gasolines consisting essentially of Carbon 0.50 to 2.50% by weight Manganese 5.00% maximum Silicon 2.00% maximum Chromium 15.00 to 30.00%

Nickel 20.00 to 35.00%

Iron 5.00% maximum Molybdenum 1.00 to 10.00% Tungsten 1.00 to 10.00% v Cobalt Substantially the balance the weight ratio of cobalt to nickel being the range from 5. An alloy composition having improved resistance to 6 burning by oxidation products of leaded gasolines consisting essentially of Carbon 0.50 to 2.50% by weight Manganese 5.00% maximum Silicon 2.00% maximum Chromium 15.00 to 30.00%

Nickel 20.00 to 35.00%

Iron 5.00% maximum Molybdenum 1.00 to 10.00% Tungsten 1.00 to 10.-00%

Cobalt Substantially the balance the weight ratio of cobalt to nickel being substantially 1:1.

6. A valve for an internal combustion engine characterized by improved resistance to burning by oxidation products of leaded gasolines consisting essentially of:

Carbon 0.50 to 2.50% by weight Manganese 5.00% maximum Silicon 2.00% maximum Chromium 15.00 to 30.00%

Nickel 20.00 to 35.00%

Iron 5.00% maximum Molybdenum 1.00 to 10.00% TungstenV 1.00 to 10.00%

Cobalt Substantially the balance the weight ratio of cobalt to nickel being at least 0.8 to l but not more than 2 to 1.

7. A valve for an internal combustion engine characterized by improved resistance to burning by oxidation products of leaded gasolines consisting essentially of:

Carbon 1.50 to 1.80% by weight Manganese 0.50% maximum Silicon 0.50% maximum Chromium 24.00 to 27.00%

Nickel 28.00 to 32.00%

Iron 3.00% maximum Molybdenum 4.00 to 7.00%

Tungsten 4.00 to 7.00%

Cobalt Substantially the balance 8. A valve for an internal combustion engine characterized by improved resistance to burning by oxidation products of leaded gasolines consisting essentially of:

Carbon 0.50 to 2.50% by weight Manganese 5.00% maximum Silicon 2.00% maximum Chromium 15.00 to 30.00%

Nickel 20.00 to 35.00%

Iron 5.00% maximum Molybdenum 1.00 to 10.00% Tungsten 1.00 to 10.00%

Cobalt Substantially the balance the weight ratio of cobalt to nickel being at least 0.8 to 1 but not more than 2 to 1, said valve being in the as cast condition and having a microstructure including dendrites separated by interdentritic carbides.

9. A valve for an internal combustion engine characterized by improved resistance to burning by oxidation products of leaded gasolines consisting essentially of:

Carbon 1.50 to 1.80% by weight Manganese 0.50% maximum Silicon 0.50% maximum v Chromium 24.00 to 27.00% Nickel 28.00 to 32.00% Iron 3.00% maximum Molybdenum 4.00 to 7.00% Tungsten 4.00 to 7.00% Cobalt Substantially the balance the weight ratio of cobalt to nickel being from 0.8 to 1.2 to 1.

10. A valve for an internal combustion engine charac- 7 terized by improved resistance to burning by oxidation products of leaded gasolines consisting essentiallykof:

Carbon 0.50 to 2.50% by weight Manganese 5.00% maximum Y r Silicon 2.00% maximum l Chromium 15.00 to 30.00%

Nickel 20.00 to 35.00%

Iron 5.00% maximumy Molybdenum 1.00 to 10.00% Tungsten 1.00 to 10.00% O Cobalt Substantially the balance the cobalt to nickel weight ratio being no more than about 2: .1, but being atleast 0.8 to 1.

1l. A valve for an internal combustion engine charac- 15 terized by improved resistance to burning by oxidation products of leaded gasolines consisting essentially of:

the cobalt to nickel weight ratio being between about 0.8

Vand 1.211.

i2. A valve for an internai combustion engine characterized by improved resistance to burning by oxidation products of leaded gasolinas consisting essentially of;

Carbon 0.50 to 2.50% by weight Manganese 5.00% maximum Silicon 2.00% maximum Chromium 15.00 to 30.00%

Nickel 20.00to'35.00%

Iron 5.00% maximum Molybdenum 1.00 to 10.00% 'Tungsten 1.00 to 10.00%

Cobalt Substantially the balance the cobalt to nickel weight ratio being substantially 1:1.

References Cited by the Examiner UNITED STATES PATENTS 2,827,373 3/58 Prassc et al. 75-171 X 2,859,149 ll/SS Straumann 75-171 3,068,096 12/62 Elbaum et al.V 75--171 FOREIGN PATENTSl SiC-,154 7/39 GrcatBritain. 53%855 i2/56 Canada. 522,451 3/59 Canada.

DAVKD L. RECK, Primary Examiner.

RAY K. WNDHAM, Examiner. 

1. AN ALLOY COMPOSITION HAVING IMPROVED RESISTANCE TO 